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What does "java.lang.NullPointerException: Attempt to invoke virtual method '...' on a null object reference" mean, and how do I solve it? [duplicate](1个答案)
8小时前关闭
我试图建立一个简单的应用程序来运行一个天文钟。一旦我编辑了我的Java代码,当我尝试运行它时,应用程序只是强制关闭。
package com.example.debatetimer;
import android.app.Activity;
import android.os.Bundle;
import android.os.SystemClock;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.Chronometer;
public class MainActivity extends Activity implements View.OnClickListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Button startbutt = (Button) findViewById(R.id.startbutton);
startbutt.setOnClickListener(this);
Button stopbutt = (Button) findViewById(R.id.stopbutton);
stopbutt.setOnClickListener(this);
Button resetbutt = (Button) findViewById(R.id.resetbutton);
resetbutt.setOnClickListener(this);
}
@Override
public void onClick(View v)
{
switch(v.getId())
{
case R.id.startbutton:{
startChronometer(v);
}
case R.id.stopbutton:{
stopChronometer(v);
}
case R.id.resetbutton:{
resetChronometer(v);
}
}
}
public void startChronometer(View view)
{
((Chronometer)findViewById(R.id.chronometer1)).start();
}
public void stopChronometer(View view)
{
((Chronometer) findViewById(R.id.chronometer1)).stop();
}
public void resetChronometer(View view)
{
((Chronometer) findViewById(R.id.chronometer1)).setBase(SystemClock.elapsedRealtime());
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
我刚刚开始自学Android,这是一个巨大的飞跃,从简单的Java。感谢所有的帮助!
2条答案
按热度按时间xytpbqjk1#
我想你忘了在你的
Activity
中设置布局,比如在
onCreate(....)
方法中和View
引用之前pcww981p2#
试试这个。
你错过了
setContentView(R.layout.layoutname);
在初始化
Button
之前添加如下内容